This circuit is for traditional old-style telephone lines found in an American 1980s documentation. Components are common and the optical coupler can be replaced with an equivalent.
We found this transistorized radio for the AM band in a Japanese publication from 1960. The...
This small source is suitable for low consumption equipment that uses batteries. The circuit is...
Found in a magazine 73 for radio amateurs, this circuit has two settings, one for the interval and the...